Add readme

Author: Ashoka de Wit

README.md

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+# Introduction
+
+This is the MediaCT coding standard for Magento 2 projects. It is a mix of the
+default MediaCT coding standard and the Magento marketplace standard.
+
+Some tests have been removed from both of the standards to create a workable
+and fast standard.
+
+# Installation
+
+Use composer to require the standard in a project.
+
+```shell
+$ composer require --dev mediact/coding-standard-magento2
+```
+
+To let PHPCS know that this standard should be used add a phpcs.xml file in the
+root of the project.
+
+```xml
+<?xml version="1.0"?>
+<ruleset>
+    <rule ref="./vendor/mediact/coding-standard-magento2/src/MediactMagento2"/>
+</ruleset>
+```
+
+# Integration with PHPStorm
+
+When the phpcs.xml file exists it will be automatically configured by
+`media/coding-standard-phpstorm`. This is triggered by the composer command.
+
+```shell
+$ composer install
+```
+
+# Contribution guidelines
+
+Contributions are welcome. Please create pull requests which add or remove
+tests.